Subterranean formations are often composed of soft shales which are relatively unstable clay-containing formations. During drilling of the well, such shales are typically dispersed as cuttings into the drilling fluid. The sloughing or influx of the shale and/or other earth formation materials into the drilling fluid is often problematic. While large drilled cuttings may be removed by solids control equipment at the surface of the wellbore, shale particles traveling in the formation typically degrade into smaller particles which can adversely result in loss of formation permeability, significant reduction in flow rate and stability of the surrounding formation. In addition, drilling time and costs are often substantially increased.
The possibility of damage caused by the swelling and migration of clay in oil and gas producing formations further poses problems during well treatment processes. For instance, the swelling and migration of formation clays, presents problems during stimulation and well completion.
While formation clays are ordinarily inert, the swelling and migration of formation clay particles is often increased when formation clays are disturbed by foreign substances, such as aqueous well treatment fluids. Such well treatment fluids include fracturing fluids. The swelling and migration of formation clay reduces the permeability of the formation by obstructing the formation capillaries and therefore resulting in a loss of formation permeability and significant reduction in the flow rate of hydrocarbons. Such obstruction results, for example, by the migration of formation clays into capillary flow channels of the formation. This, in turn, typically causes significant reduction in the flow rate of produced hydrocarbons.
Attempts to diminish the damaging effects caused by the swelling and migration of formation clays has included the use of aqueous well treatment fluids containing one or more additives. For instance, clay disintegration in drilling fluids is often effectuated by the use of drilling fluids containing one or more shale inhibitors. In other well treatment fluids, such as stimulation fluids and remedial fluids, a clay stabilizer is included.
Shale inhibitors and clay stabilizers are known to stabilize clay formation materials. They work on the principle of substitution of a cationic species in the clay lattice for a sodium ion. The cationic species is generally selected such that its radius of hydration is less than that of the sodium ion. It is believed that the molecules of shale inhibitors and clay stabilizers become adsorbed onto the surface of the clay and compete with molecules of water for reactive sites. Thus, the possibility of swelling and migration in the formation clay is minimized upon contact of the formation clay with a foreign, or well treatment, fluid. As a result, the probability of disintegration of formation clays is diminished. In addition, stabilization of the formation clay inhibits clay swelling.
Potassium chloride is widely used as a shale inhibitor and/or clay stabilizer. In stimulation methods, potassium chloride has often been used as a preflush and/or added to aqueous stimulation fluids in order to convert the clay to a less swellable form. While such salts diminish the reduction of formation permeability, they are often detrimental to the performance of other constituents of the well treatment fluid. For example, high concentration of such salts is typically required for stabilization of clay (typically 3%). Such salts further produce high chloride levels which are environmentally unacceptable.
While other alternatives have been reported in the literature, they too are often undesirable because of their potent odor and/or poor effectiveness in formations with low permeability.
Alternative materials have therefore been sought, especially for use in drilling, fracturing and work over procedures. It is desirable that such alternative materials have low toxicity levels and minimize environmental pollution and harm to operators. In addition, it is desirable that such alternative materials not inhibit the performance of other additives in the well treatment fluid.